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[en] Highlights: • N-enriched carbon nanofiber webs are prepared via direct carbonization route with polyporrole as template. • The pyrolysis time plays an important role in N doping level and existing type. • Effect of N-doping on performance of the carbon anode material is investigated. • High reversible capacity of 238 mAh g−1 at 5 A g−1 is attained. -- Abstract: Nitrogen-doped carbon nanofiber webs (N-CNFWs) are prepared by direct pyrolyzation of polypyrrole (PPy) nanofiber webs at 600 °C. The structure and morphology of N-CNFWs are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Raman spectra and elemental analysis. Both the doped N content and the N existing type in carbon, change with the pyrolysis time. As anode material for lithium-ion battery, the N-CNFWs show high capacity and good rate capability. The reversible capacity is up to 668 mAh g−1 at a current density of 0.1 A g−1 and 238 mAh g−1 at 5 A g−1, which can be ascribed to the nanofiber structure and high nitrogen content
[en] Highlights: • A flexible, robust paper electrode serves as an efficient sulfur host for Li-S batteries. • The electrode with high sulfur loading exhibits superior cycling stability at high rates. • The long cycle life also stems from a stable lithium-metal anode. Fast capacity degradation and low sulfur loading hamper lithium-sulfur batteries from practical application. We present here a flexible and robust paper electrode consisting of carbon nanotubes (CNT) and activated carbon nanofibers (ACNF) loaded with MnO2 nanosheets to serve as an efficient sulfur host for Li/dissolved polysulfide batteries. This integrally-designed flexible host facilitates high sulfur loading, improves sulfur utilization, and suppresses effectively the parasitic shuttle. Accordingly, the Li/dissolved polysulfide cells with high sulfur loading exhibit a high-rate capacity of 780 mAh g−1 at 2 C rate and a high capacity retention of 64% over 300 cycles, demonstrating great promise for practical applications of Li-S batteries. In addition, a stable lithium-metal anode resulting from the suppressed shuttle effect is also proved to contribute significantly to the promising cycling performance.
[en] Metal-air batteries, especially Li-air batteries, have attracted significant research attention in the past decade. However, the electrochemical reactions between CO_2 (0.04 % in ambient air) with Li anode may lead to the irreversible formation of insulating Li_2CO_3, making the battery less rechargeable. To make the Li-CO_2 batteries usable under ambient conditions, it is critical to develop highly efficient catalysts for the CO_2 reduction and evolution reactions and investigate the electrochemical behavior of Li-CO_2 batteries. Here, we demonstrate a rechargeable Li-CO_2 battery with a high reversibility by using B,N-codoped holey graphene as a highly efficient catalyst for CO_2 reduction and evolution reactions. Benefiting from the unique porous holey nanostructure and high catalytic activity of the cathode, the as-prepared Li-CO_2 batteries exhibit high reversibility, low polarization, excellent rate performance, and superior long-term cycling stability over 200 cycles at a high current density of 1.0 A g"-"1. Our results open up new possibilities for the development of long-term Li-air batteries reusable under ambient conditions, and the utilization and storage of CO_2. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] For Li-Se batteries, ether- and carbonate-based electrolytes are commonly used. However, because of the ''shuttle effect'' of the highly dissoluble long-chain lithium polyselenides (LPSes, LiSe, 4≤n≤8) in the ether electrolytes and the sluggish one-step solid-solid conversion between Se and LiSe in the carbonate electrolytes, a large amount of porous carbon (>40 wt % in the electrode) is always needed for the Se cathodes, which seriously counteracts the advantage of Se electrodes in terms of volumetric capacity. Herein an acetonitrile-based electrolyte is introduced for the Li-Se system, and a two-plateau conversion mechanism is proposed. This new Li-Se chemistry not only avoids the shuttle effect but also facilitates the conversion between Se and LiSe, enabling an efficient Se cathode with high Se utilization (97 %) and enhanced Coulombic efficiency. Moreover, with such a designed electrolyte, a highly compact Se electrode (2.35 g cm) with a record-breaking Se content (80 wt %) and high Se loading (8 mg cm) is demonstrated to have a superhigh volumetric energy density of up to 2502 Wh L, surpassing that of LiCoO. (© 2020 Wiley‐VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] Nonstoichiometry and Na incorporation are designed to attain controllable impurity phases Li4P2O7 and Li3PO4 in LiFePO4. The effects of Li4P2O7 and Li3PO4 on structure and electrochemical performance have been investigated. Both Li4P2O7 and Li3PO4 impurities are observed in (Fe, P)-deficient LiFe0.9P0.95O4−δ. With Na+ incorporation, Li4P2O7 phase disappears while Li3PO4 content increases. Proved by X-ray photoelectron spectroscopy, nonstoichiometry and Na-incorporation do not change the chemical state of Fe(II). Our experiments indicate that Li4P2O7 and Li3PO4 show different effects on the electrochemical performance. Li4P2O7 leads to degradation of cyclability, whereas a small amount of Li3PO4 is beneficial for the improvement in capacity and rate capability. The 1% Na-doped LiFe0.9P0.95O4−δ composite exhibits the best electrochemical performance. We ascribe the improvement to the structural stabilization caused by the existence of Li3PO4.